Immuno-electrophoretic and chromatographic techniques are being used to characterize and purify the amastigote-trypomastigote antigens prepared from cell cultures infected with T. cruzi. This cell culture antigen has at least one or more immunologically active fractions that are different from conventional epimastigote antigens. The methods used to characterize infectivity of different strains or passage lines of T. cruzi for cells in vitro include determination of minimum infective unit by terminal dilution titration and by plaque formation, and two or three-cycle growth curves. The plaquing technique requires more technical evaluation, but the infectivity titration and growth curve determinations are reproducible. On the basis of these tests cryopreservation of T. cruzi results in biologic changes of the organism. Leishmanial infection (L. tropica) in the genetic inbred mouse was found to be inhibited by prior BCG infection. Extracts from leishmanial promastigotes were found to be mitogenic for mouse B cells. The nature of the genetic pattern characterization is underway. BIBLIOGRAPHIC REFERENCES: Neva, F.A. and Gam, A.A.: A complement-fixing antigen from Trypanosoma cruzi grown in cell cultures. Am. J. Trop. Med. & Hyg. 26: 37-46, 1977. Gam, A.A. and Neva, F.A.: Comparison of cell culture with epimastigote antigens of Trypanosoma cruzi. Am. J. Trop. Med. & Hyg. 26: 47-57, 1977.